Add chart filter user attribute documentation (#396)

Documents the new chart filter feature that allows using ${lightdash.user.email} and ${lightdash.attribute.<name>} in filter values. This enables dynamic filtering based on the logged-in user's attributes.

---

Created by Mintlify agent

Author: mintlify[bot]

references/workspace/user-attributes.mdx

@@ -52,6 +52,10 @@ User attributes can be used in these specific contexts within the model.yaml fil
 - `any_attributes:` - For column and table access control (OR logic - at least one condition must match)
 - `sql_on:` - For filtering joins
 
+User attributes can also be used in:
+
+- **Chart filter values** - Filter charts dynamically based on the logged-in user
+
 <Info>
   User attributes cannot currently be referenced inside`sql:` tags within the model YAML files.
 </Info>
@@ -107,6 +111,23 @@ When referencing user attributes in SQL you can use the following [SQL variables
   If you are self hosting you can enable [SMTP](/self-host/customize-deployment/configure-smtp-for-lightdash-email-notifications) or [SSO](/self-host/customize-deployment/use-sso-login-for-self-hosted-lightdash) authentication to allow users to verify their email address.
 </Info>
 
+### Using user attributes in chart filter values
+
+You can reference user attributes directly in chart filter values to create dynamic filters based on the logged-in user. This is useful for creating charts that automatically filter to show only data relevant to the current user.
+
+To use a user attribute in a filter value, enter one of the following references:
+
+- `${lightdash.user.email}` - The logged-in user's email address
+- `${lightdash.attribute.<attribute_name>}` - A custom user attribute value
+
+For example, if you have a chart showing sales data and you want each user to only see their own records, you can add a filter where `sales_rep_email` is equal to `${lightdash.user.email}`. When the chart runs, the filter value will be replaced with the actual email of the logged-in user.
+
+Similarly, you can use custom attributes like `${lightdash.attribute.country}` to filter data based on a user's assigned region or department.
+
+<Info>
+  If a user attribute referenced in a filter value is not set for the current user, the query will return a `Forbidden` error.
+</Info>
+
 ### Row filtering with `sql_filter`
 
 Row-level security (RLS) in Lightdash is implemented using the `sql_filter` property combined with user attributes. This allows you to restrict which rows each user can see based on their attributes.
@@ -637,4 +658,4 @@ Let's walk through an example:
   </Tab>
 </Tabs>
 
-In this example, the `${lightdash.attributes.fruit}` will be replaced with `'kiwi','orange','coconut'`. The final SQL will be `my_model.fruit IN ('kiwi','orange','coconut)`
+In this example, the `${lightdash.attributes.fruit}` will be replaced with `'kiwi','orange','coconut'`. The final SQL will be `my_model.fruit IN ('kiwi','orange','coconut)`